The strangest error I've had in Vista was that one day, out of the blue, a bunch of my shortcuts re-linked to themselves.
So, one day I tried to open up MS Word, only to find that it wouldn't open. Why? The shortcut had somehow changed to open, not MS Word, but the shortcut itself. All of my Office programs had this happen. Also, because the shortcuts weren't technically "broken," Vista didn't open the "searching for missing program" box to fix it for me.
I tried finding the *.exe files the shortcuts should have been linked to, but couldn't find a couple (Access I think was one of them), so I wasn't able to fix it that way.
So then I tried to reinstall Office to fix the problem. I then found that Office cannot be reinstalled once it has been installed once. I then tried to uninstall Office, which gave me an error. I ended up having to manually uninstall Office using a guide on Microsoft's help page, just to reinstall it, just to fix the stupid shortcuts.
Other than that, Vista has worked tolerably well for me.